I have created a file in /etc/ssh/certs and named it dhparam.pem (I also tried ffdhe4096.txt). And added the parameters in it. In /etc/letsencrypt/options-ssl-apache.com I have added the line: SSLOpenSSLConfCmd DHParameters /etc/ssl/certs/dhparam.pem and restarted apache.
I have tried different locations and names without luck.
This is my cypherlist: ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-RSA-CHACHA20-POLY1305:DHE-RSA-AES128-GCM-SHA256:DHE-RSA-AES256-GCM-SHA384